Configuring EIGRP for the CCNA is easy. In fact, there are only a few commands that you need to know. You should be aware of the goal of the configuration first. Assume you are required to enable the protocol using Autonomous System 100 and that peers on interface Serial 0/0/0 should authenticate each other using MD5.

Just break it down:

Enable the EIGRP protocol:

router eigrp 100

Then define the networks to participate in EIGRP routing:

network 10.0.0.0
network 192.168.1.0

Next create the key-chain to be used for authentication in global configuration mode:

key-chain eigrpkey
key 1
key-string cisco123

Now enable the authentication process on the serial interface. Make sure this matches on both sides of the link otherwise you will not form up a neighbor:

ip authentication mode eigrp 100 md5
ip authentication key-chain eigrp 100 eigrpkey

Thats it! You are in business. To verify use the following commands:

show ip eigrp neighbors


----- look for a neighbor on the interface that you
setup authenticaiton for.

show ip route

--- look for routes marked "D"

show ip protocols

--- look for eigrp to be enabled and routing for the proper
networks